This invention is related generally to propulsion units for boats and, more particularly, to marine jet drives.
Marine jet drives which propel vessels by means of water jets have long been known and used, and have certain significant advantages over the traditional external propeller units. A typical marine jet drive includes an engine-driven impeller which rotates inside an impeller housing. The impeller pumps water from below the vessel through an intake duct, and then pressurizes and expels the water through a diffusor housing and a nozzle behind the vessel.
Marine jet drives of the prior art have a number of problems and shortcomings, including as set forth below:
Design of marine jet drives involves many engineering considerations, such as: overall weight; tensile strength, compression, shear strength, elasticity, expansion and corrosivity of materials; operational tolerances; alignment considerations; and effective use of vessel space. Under the varying loads of operation of any marine jet drive, the propulsion system undergoes varying amounts of deformations. Engines, by virtue of the fact that they are typically mounted on resilient motor mounts, also produce movement which must be accommodated. Given these factors, it is necessary that marine jet drive systems accommodate such movements and deformations in one way or another.
Conventional jet drives need impeller tip clearances which are sufficient to allow for various deformations (including intake-duct deformation), engine-mount movement, shaft flexing and relative bearing movement under operational loads. In marine jet drive systems, the requirement of a water intake between the engine and the impeller typically means that the drive shaft, which extends across a portion of the intake duct, have considerable length. It is known that long unsupported spans of drive shafts require greater impeller-tip clearances than a shorter and/or supported spans of drive shafts. Larger impeller-tip clearances dramatically reduce the efficiency of jet drives.
The conventional jet drive, which has a drive shaft exposed to water in the intake duct, requires a shaft seal where the drive shaft passes through the transom (from the intake duct into the engine compartment within the vessel) in order to prevent ingress of water into the vessel. However, to avoid compromising such seals, drive shaft movement due to resilient motor mounts or deformation must be controlled. Drive shaft movement is typically restrained by a bearing and support structure between the engine and shaft seal assembly. Such bearing and seal assembly take up valuable vessel space by requiring that the engine be placed farther forward than would otherwise be necessary.
Use of metal structures has been considered favorable for reasons of strength and deformation resistance. However, use of metal parts in water, particularly sea water, produces electrolysis and corrosion, which have deleterious effects on longevity of conventional jet drives, on efficiency of operation, and in various other ways. Use of metal parts also contributes to high weight which has negative implications for performance.
Another prior art problem is the tendency of waterborne debris, particularly long-stranded debris, to become wrapped around exposed rotating drive shafts and impellers of conventional jet drives. This tends to reduce efficiency of operation, and can immobilize and endanger a vessel, particularly when its engine is turned off to clear the debris.
Another problem in various conventional marine jet drives is that they require frequent servicing and repair, and their disassembly is time-consuming.
It is accordingly a primary object of the present invention to provide a marine jet drive propulsion system that overcomes problems and shortcomings of the prior art, including those set forth above.
Another object of the invention is to provide an improved marine jet drive which readily accommodates a substantial degree of misalignment due to movements and deformations during system operation and a greater variation in engine placement.
Another object of the invention is to provide an improved marine jet drive which more effectively utilizes vessel space by allowing engine placement in a position which is farther aft.
Another object of the invention is to provide an improved marine jet drive in which the drive shaft is protected from exposure to water.
Another object of the invention is to provide an improved marine jet drive which is protected from entanglement of long-stranded debris with the drive shaft.
Another object of the invention is to provide an improved marine jet drive which protects the impeller from entanglement with long-stranded debris.
Another object of the invention is to provide an improved marine jet drive allowing a wider selection of materials, including drive-shaft materials.
Still another object of this invention is to provide an improved marine jet drive having a reduced unit weight.
Another object of the invention is to provide an improved marine jet drive which is easily and quickly serviced.
These and other objects of the invention will be apparent from the following descriptions and from the drawings.
This invention is an improved marine jet drive which overcomes various problems and shortcomings of the prior art including those referred to above. The marine jet drive of this invention is of the type which has forward and rearward ends, a rotatable impeller, an impeller housing around the impeller, a wall structure defining an intake duct forward of the impeller, a diffusor housing rearward of the impeller housing, an engine, and a unitary drive shaft extending from the engine to the impeller.
The improved marine jet drive of this invention includes a rear flexible coupling flexibly connecting the drive shaft to the impeller, and a front flexible coupling flexibly connecting the drive shaft to the engine. In preferred embodiments, the front flexible coupling is inside the vessel and directly coupled to the engine.
In preferred embodiments, the marine jet drive includes a bearing support structure which is disposed inside the diffusor housing and rotatively supports the impeller, and the rear flexible coupling is disposed within such bearing support structure. The bearing support structure is preferably rigidly attached to the diffusor housing by a plurality of radially disposed stator vanes.
In certain embodiments, the rear flexible coupling includes a drive shaft tube having at least one key for connection to the impeller, and the drive shaft is flexibly connected to the drive shaft tube by the rear flexible coupling.
Highly preferred embodiments include a shaft sleeve secured with respect to the duct-forming wall structure and having front and rear sleeve ends, and a seal assembly at the rear end of the shaft sleeve, such that the drive shaft is isolated from water and debris. In such highly preferred embodiments, the seal assembly preferably includes a seal cartridge between the shaft sleeve and the impeller.
In certain of such highly preferred embodiments, the impeller includes an impeller hub and a rotating outer housing member secured with respect to the impeller hub, and the seal assembly includes such outer housing member and the seal cartridge which is within the outer housing member. The seal cartridge preferably includes: a rotating seal element; a static seal element contacting the rotating seal element, the rotating and static seal elements have sealing faces engaged with one another; an inner housing member adjacent to and enclosing a portion of the static seal element and in releaseable sealing engagement with the shaft sleeve; and a spring extending between the inner housing member and the static seal element to urge the static seal element against the rotating seal element.
In highly preferred embodiments of the type just described, the inner housing member is retained within the outer housing member by an annular-groove-and-pin arrangement which allows free rotation of the outer housing member about the inner housing member but prevents the inner housing member from being axially separated from the outer housing member, thus retaining the seal cartridge in position during installation or disassembly of the drive unit from the vessel. Such annular-groove-and-pin arrangement most preferably involves the inner housing member having an outer surface with an annular groove on it, and at least one (and preferably more than one) retaining pin through the outer housing member and extending part way into the annular groove. The retaining pin or pins can be withdrawn from the annular groove to allow removal of the seal cartridge from the outer housing member.
In certain of the preferred embodiments having a shaft sleeve and rear seal to isolate the drive shaft, the shaft sleeve has a rear recess and the inner housing member referred to above has a forward portion which is removably inserted into the rear recess, the forward portion having a compressible seal engaging the shaft sleeve within the rear recess. This serves to provide sealing engagement while permitting release of the seal cartridge when an axial pull is applied to quickly and easily separate the inner housing from the shaft sleeve.
In certain of the preferred embodiments having a shaft sleeve and rear seal to isolate the drive shaft, the above-mentioned rotating outer housing member in which the seal cartridge is located has one or more radially-disposed ports therethrough which are adjacent to the static seal element. This allows the centrifugal action caused by rotation of the outer housing member to cause water to be drawn past the static seal element and out through the ports to facilitate cooling of the sealing surfaces. It is most preferred that the static seal element include cooling fins to facilitate heat transfer from the seal elements to the flowing water. This helps to keep the interfacing rotating and static seal elements from overheating.
Certain of the preferred embodiments that have a shaft sleeve and rear seal to isolate the drive shaft also include a debris-cutting device which serves to sever and reduce long-stranded incoming debris in order to prevent deleterious interactions with the impeller. The debris-cutting device includes one or more rotating blades which are secured to the outer housing member and at least one fixed blade secured with respect to the shaft sleeve in position such that the rotating blade or blades rotate past the fixed blade(s) to sever debris.
The marine jet drive dual-flexible-coupling arrangement of this invention provides important advantages. Significantly, such improved marine jet drives are particularly excellent in their accommodation of substantial deformation and movements which occur in jet-drive operation, allowing a jet drive to accommodate a variety of vessels and engines. The invention also facilitates assembly and disassembly of the drive unit with respect to the engine.
The preferred embodiments which also include a shaft sleeve and rearward seal assembly to isolate the drive shaft from water and debris provide various further advantages. For example, a wider choice of drive-shaft sizes and materials is allowed, and this facilitates weight reduction and enhances performance. In addition, isolation of the drive shaft from the water eliminates any entanglement of debris with the drive shaft, and all the related problems. Versions including a debris cutter further protect the impeller from such debris.